A header for an implantable medical device includes at least an antenna and a receptacle for receiving a signal transmission line. Either one or a combination of the antenna and the receptacle are encased in a dielectric material. The dielectric material can be one of or include one of a polymer, a ceramic material, polyoxymethylene, polysulfone, polybutylene terephthalate. A medical device and a method for assembling a medical device are also provided.